The present invention relates to a power roller bearing for use in a toroidal type continuous variable transmission system used as a transmission of an automobile or the like.
A toroidal type continuous variable transmission system, which has been conventionally developed mainly as a transmission of an automobile, comprises a toroidal type transmission mechanism structured such that input and output disks with their respective mutually opposing faces having an arc-shaped cross section are combined with a power roller rotatably held by and between the input and output disks. The input disk is drivably connected to a torque input shaft in such a manner that it can be moved in a torque input shaft direction and, on the other hand, the output disk is mounted opposed to the input disk in such a manner that it can be relatively rotated with respect to the torque input shaft and is limited in the movement thereof in a direction where it moves away from the input disk.
In the above-mentioned toroidal type transmission mechanism, if the input disk is rotated, then the output disk is rotated in the opposite direction through the power roller, so that a rotational motion input to the torque input shaft is transmitted to the output disk as an opposite-direction rotational motion and is then taken out there. In this transmission, if the inclination angle of the rotary shaft of the power roller is caused to vary in such a manner that the peripheral face of the power roller can be contacted not only with the adjoining portion of the outer periphery of the input disk and but also with the adjoining portion of the center of the output disk, then the rotational motion to be transmitted from the torque input shaft to an output gear can be increased in speed; and, on the other hand, if the inclination angle of the rotary shaft of the power roller is caused to vary in such a manner that the peripheral face of the power roller can be contacted not only with the adjoining portion of the center periphery of the input disk and but also with the adjoining portion of the outer periphery of the output disk, then the rotational motion to be transmitted from the torque input shaft to the output gear can be reduced in speed. Further, by controlling the inclination angle of the rotary shaft of the power roller properly, intermediate transmission ratios between the above conditions can also be obtained in an almost continuously variable manner.
The power roller is coupled to a trunnion to be mounted on a casing of the toroidal type continuous variable transmission system through a pivot shaft having a torsional position relation with respect to the torque input shaft, while the inclination angle of the power roller can be adjusted according to the swing motion of the trunnion about the pivot shaft. Between the power roller and trunnion, to keep the power roller in a freely rotatable manner, there is disposed a power roller bearing such as a thrust rotary shaft bearing or the like.
The power roller is composed of a bearing outer race and a plurality of rolling elements (here, balls); and, these rolling elements can be rolled in the circumferential direction thereof while they are held by and between the power roller and bearing outer race. To guide the rolling elements, on both of the back face of the power roller and the opposed face of the bearing outer race to the power roller, there are formed race grooves extending in the circumferential direction, while each race groove is formed in a circular shape. Also, in order that the rolling elements are respectively allowed to roll along their associated race grooves while being kept properly spaced from each other, there is combined such a hollow disk-shaped cage 1 as shown in FIG. 1. On the cage 1, there are formed a plurality of circular-shaped pocket holes 5 which are respectively so disposed as to correspond to the positions of the race grooves and extend in the thickness direction of the cage, while the rolling elements are disposed between the race grooves of the power roller and the bearing outer race in such a manner that they are rollably held in their respective circular-shaped pocket holes 5. By the way, in the structure shown in FIG. 5, since the rolling elements are balls, the pocket holes 5 are respectively formed in a circular shape. However, when the rolling elements are rollers or needle-like rollers, there may be formed pocket holes which are respectively formed in a proper shape corresponding to such rolling elements.
Since the above-mentioned power roller rotates at high speeds and transmits a drive force during the operation of the toroidal type continuous variable transmission system, the power roller bearing supporting such power roller requires high durability and reliability.
In the toroidal type continuous variable transmission system, when transmitting a large torque, a load applied to the power roller becomes excessively large. As a result of this, as shown in FIG. 2, a trunnion 11 supporting a power roller 10 is deformed to thereby generate a bending moment f in an arrow direction in FIG. 2; that is, the bending moment f is applied to an outer race 12 of a power roller bearing connected to the trunnion 11 to press and deform the same. If the outer race 12 of the power roller bearing is given the bending moment f from the trunnion 11 and is thereby deformed, then there cannot be obtained the smooth rolling movements of rolling elements 6 which are respectively disposed in their associated pocket holes.
Now, FIGS. 3 and 4 are respectively explanatory diagrams of the deformed state of the power roller bearing outer race 12 caused by the abovementioned reason. In particular, FIG. 3 shows an outer race 12a of the power roller bearing before it is deformed and FIG. 4 shows an outer race 12b of the power roller bearing after it is deformed, respectively viewed from the rotary shaft direction of the power roller 10. In FIGS. 3 and 4, the respective loci of the inside diameter side edge and outside diameter side edge of the race groove along which the rolling elements 6 are allowed to roll are denoted by dashed lines. Due to the influence of the bending moment f applied to the power roller bearing outer race 12 from the trunnion 11, the loci thereof respectively having an almost complete circular shape as shown in FIG. 3 are changed into those having an elliptical shape as shown in FIG. 4.
On the other hand, the bending moment f from the trunnion 11 is applied little onto the cage 1 of the power roller bearing which is not connected directly to the trunnion 11. For this reason, the power roller bearing cage 1 keeps its original shape approximate to a complete circular shape as it is; that is, similarly before the trunnion 11 is deformed, the cage 1 is going to maintain the rolling loci of the rolling elements 6 in their original shapes, or, in the complete circular shapes.
Owing to the combination of the thus deformed bearing outer race 12 with the cage maintaining its complete circular shape, the rolling elements 6 within the pocket holes 5 are respectively caused to roll along the complete circular shape within the race grooves deformed into the elliptical shapes, so that an excessive force is applied to the respective rolling elements 6. As a result of this, the rolling movements of the respective rolling elements 6 are extremely restricted to thereby cause the contact portions not only between the rolling elements 6 and bearing outer race 12 but also between the rolling elements 6 and cage to slip. Since the deterioration of the transmission efficiency caused by the slippage of the rolling elements 6 increases the power loss, the deformation of the trunnion 11 gives rise to the lowered reliability of the whole toroidal type continuous variable transmission system. Also, in this case, the peripheral faces of the rolling elements 6 and the respective race grooves suffering from the excessive forces are very easy to be worn and damaged; that is, such wear and damage provide the cause for the shortened life of the power roller bearing.
On the other hand, as a transmission for an automobile, it has been studied to use such a toroidal type continuous variable transmission system as shown schematically in FIGS. 5 and 6. In this toroidal type continuous variable transmission system, for example, as disclosed in Japanese Utility Model Publication No. Sho. 62-71465, an input side disk 102 is supported coaxially with an input shaft 101 and an output side disk 104 is fixed to the end portion of an output shaft 103. And, on the inner face of a casing in which the toroidal type continuous variable transmission system is stored, or on a bracket provided in the interior portion of the present case, there are disposed trunnions 106 which can be respectively swung about pivot shafts 105 having torsional position relations with respect to the input shaft 101 and output shaft 103.
The respective trunnions 106 include the pivot shafts 105 on the outside faces of their respective two side end portions. Also, the base end portions of shift shafts 107 are supported on the respective central portions of the two trunnions 106. That is, with use of this structure, if the terunnions 106 are respectively swung about the pivot shafts 105, then the inclination angles of the shift shafts 107 can be adjusted freely. Further, two power rollers 108 are rotatably supported on the respective peripheries of the shift shafts 107 respectively supporting the trunnions 106. And, the two power rollers 108 are held by and between the input side and output side disks 102 and 104. While the input side and output side disks 102 and 104 respectively include inside faces 102a and 104a which are opposed to each other, each of the inside faces 102a and 104a includes a cross section which is formed as an arc-shaped concave face with its associated pivot shaft 105 as the center thereof. And, the peripheral faces 108a of the power rollers 108, which are respectively formed as spherical convex faces, are in contact with the inside faces 102a respectively.
Also, between the input shaft 101 and input side disk 102, there is interposed a pressing device 109 of a loading cam type, while the pressing device 109 elastically presses against the input side disk 102 toward the output side disk 104. The pressing device 109 is composed of a cam plate 110 rotatable together with the input shaft 101 and a plurality (for example, four pieces) of rollers 112 respectively held by a cage 111. On one side face (in FIGS. 5 and 6, on the left face) of the cam plate 110, there is formed a cam face 113 which is a concavo-convex (that is, wavingly curved) face extending in the circumferential direction of the cam plate 110 and, on the outside face (in FIGS. 5 and 6, on the right face) of the input side disk 102 as well, there is formed a similar cam face 114. And, the above-mentioned plurality of rollers 112 are supported in such a manner that they can be rotated about their own axes which respectively extend in the radial direction with respect to the center of the input shaft 1.
When the above-structured toroidal type continuous variable transmission system is in operation, if the cam plate 110 is rotated in linking with the rotation of the input shaft 101, then the cam face 113 presses the plurality of rollers 112 against the cam face 114 of the outside face of the input side disk 102. As a result of this, the input side disk 102 is pressed against the plurality of power rollers 108 and, at the same time, due to the mutual pressing contact of the pair of cam faces 113 and 114 with the plurality of rollers 112, the input side disk 102 is rotated. And, the rotation of the input side disk 102 is transmitted through the plurality of power rollers 108 to the output side disk 104, so that the output shaft 103 fixed to the output side disk 104 can rotated.
Now, description will be given below of a case in which the rotation speeds of the input shaft 101 and output shaft 103 are to be changed. At first, to reduce the rotation speed between the input shaft 101 and output shaft 103, the trunnions 106 are swung in a predetermined direction about their respective pivot shafts 105. And, as shown in FIG. 5, the shift shafts 107 are respectively inclined in such a manner that the peripheral faces 108a of the power rollers 108, 108 can be respectively brought into contact not only with the portion of the inside face 102a of the input side disk 102 that is located near the center thereof but also with the portion of the inside face 104a of the output side disk 104 that is located near the outer periphery thereof. On the other hand, to increase the rotation speed, the trunnions 106 are swung in the opposite direction to the predetermined direction. And, as shown in FIG. 6, the shift shafts 107 are respectively inclined in such a manner that the peripheral faces 108a of the power rollers 108 can be respectively brought into contact not only with the portion of the inside face 102a of the input side disk 102 that is located near the outer periphery thereof but also with the portion of the inside face 104a of the output side disk 104 that is located near the center thereof. By the way, if the inclination angles of the shift shafts 107 are respectively set in the intermediate range between FIGS. 5 and 6, then intermediate transmission ratios can be obtained between the input shaft 101 and output shaft 103.
Further, FIG. 7 shows a toroidal type continuous variable transmission system disclosed in a microfilm of Japanese Utility Model Application Nos. Sho. 61-87523 and Sho. 62-199557, which proposes a more concrete structure as a transmission of an automobile. In this structure, the rotation of a crank shaft of an engine is transmitted through a clutch 115 to an input shaft 116 to thereby rotate a cam plate 110 which is spline engaged with the middle portion of the input shaft 116, so that a pressing device 109 including the cam plate 110 is actuated. And, due to the actuation of the pressing device 109, an input side disk 102 is rotated while it is being pressed in the left direction in FIG. 7 toward an output side disk 104. The rotation of the input side disk 102 is transmitted through power rollers 108 to the output side disk 104.
The output side disk 104 is supported by a needle bearing 117 on the periphery of the input shaft 116. Also, a cylindrical output shaft 118 formed integrally with the output side disk 104 is supported in the interior portion of a housing 119 by a ball bearing 120 of an angular contact type. On the other hand, one end (in FIG. 7, the right end) of the input shaft 116 is rotatably supported in the interior portion of the housing 119 by a roller bearing 121, while the other end thereof is rotatably supported in the interior portion of the housing 119 by a ball bearing 122 through a sleeve 123.
Also, a transmission gear 126, which is composed of a drive side advancing gear 124 and a drive side retreating gear 125 formed integrally with each other, is spline engaged with the outer peripheral face of the output shaft 118. When advancing an automobile, the transmission gear 126 is moved to the right in FIG. 7 to thereby bring the drive side advancing gear 124 into direct meshing engagement with a driven side advancing gear 128 which is provided in the middle portion of a take-out shaft 127. On the other hand, when retreating the automobile, the transmission gear 126 is moved to the left in FIG. 7 to thereby bring the drive side retreating gear 125 into meshing engagement with a driven side retreating gear 129 through an intermediate gear (not shown), while the driven side retreating gear 129 is fixed to the middle portion of the take-out shaft 27.
When the toroidal type continuous variable transmission system structured in the above-mentioned manner is in use, if the input shaft 116 is rotated through the clutch 115 by the engine to thereby move the transmission gear 126 in a proper direction, then the take-out shaft 127 can be rotated in an arbitrary direction. Also, if trunnions 106 are respectively swung to thereby change the contact positions between the peripheral faces 108a of the power rollers 108 and the inside faces 102a, 104a of the input side and output side disks 102, 104, then the rotation speed ratios between the input shaft 116 and take-out shaft 127 can be changed.
When the above-mentioned toroidal type continuous variable transmission system is in operation, by means of the operation of the pressing device 109, the input side disk 102 is pressed toward the output side disk 104. As a result of this, to the input shaft 116 supporting the cam plate 110 forming the pressing device 109, there is applied a thrust load going in the right direction in FIG. 7 as a reaction caused by the above pressing operation. The thrust load is received by the ball bearing 122 through not only a nut 130 which is engaged with the end portion of the input shaft 116 but also the sleeve 123. Also, due to the operation of the pressing device 109, a thrust load going in the left direction in FIG. 7 is applied to the output shaft 118 through the input side and output side disks 102 and 104 as well as through the power rollers 108. The thrust load is carried by the ball bearing 120 through a stop ring 31 which is fitted with the outside portion of the output shaft 118.
Also, when the above-mentioned toroidal type continuous variable transmission system is in operation, not only the thrust loads are respectively applied to the input shaft 116 and output shaft 118, but also thrust loads are applied to the power rollers 108 as well. Therefore, thrust rolling bearings 132, 132 are respectively interposed between the power rollers 108, 108 and trunnions 106, 106, so that the thrust loads applied to the power rollers 108, 108 can be received by these thrust rolling bearings 132. Each of the thrust rolling bearings 132 includes a plurality of rolling elements 133, a cage 134 which is used to hold the plurality of rolling elements 133 in a freely reliable manner, and an outer race 135. Each of the rolling elements 133 is formed of bearing steel or ceramics in a spherical shape or in a tapered roller shape. The rolling elements 133 can be rollingly contacted not only with race faces (inner race faces) formed on the outer end faces of the power rollers 108 but also with race faces (inner race faces) formed on the inner faces of the outer races 135. Also, the cage 134 is formed of metal or synthetic resin in a circular ring shape, and includes a plurality of pockets 136 which are respectively formed in the middle portion thereof in the diameter direction thereof at positions equally spaced in the circumferential direction thereof, while the rolling elements 133 are retained in these pockets 136, one rolling element in each pocket. Further, the outer races 135, which are formed of bearing steel or ceramics in a circular ring shape, are butted against the inside faces of the trunnions 106 through thrust bearings 137 (see FIG. 8 which will be discussed below), respectively.
The above-structured thrust rolling bearings 132, when the toroidal type continuous variable transmission system is in operation, rotate at high speeds while supporting the thrust loads applied onto the power rollers 108. For this reason, when the toroidal type continuous variable transmission system is in operation, a sufficient amount of lubrication oil must be supplied to the thrust rolling bearings 132. In view of this, conventionally, there has been proposed a lubrication method in which, as shown in FIG. 8, one or more oil supply holes 138 are formed in part of the outer race 135 and, when the toroidal type continuous variable transmission system is in operation, the lubrication oil is forcibly supplied into these oil supply holes 138. The lubrication oil forcibly supplied into the oil supply holes 138 is allowed to flow through gaps between the inner faces of the outer races 135 and the outer faces of the cages 134 as well as through gaps between the inner faces of the cages 134 and the outer end faces of the power rollers 108; that is, during such flow, the lubrication oil lubricates the rolling portions of the rolling elements 133.
By the way, in the structure for supplying the lubrication oil to the thrust rolling bearing 132 in the above-mentioned manner, there is a possibility that supply of the lubrication can be short in part. That is, as shown in FIG. 9(A), if the cage 134 is situated between the inner face of the outer race 135 and the outer end face of the power roller 108, then the lubrication oil flows not only into the gap between the inner face of the outer race 135 and the outer face of the cage 134 but also into the gap between the inner face of the cage 134 and the outer end face of the power roller 108; that is, in this case, there arises no problem. However, if the lubrication oil is discharged toward the outer face of the cage 134 from the oil supply hole 138, then the cage 134 is pushed by the flow of the lubrication oil, so that, as shown in FIG. 9(B), the cage 134 is shifted in position to the power roller 108 side. If the inner face of the cage 134 and the outer end face of the power roller 108 are closely contacted with each other due to such position shift of the cage 134, then a sufficient amount of lubrication oil is not present in the contact portion between the race face formed in the present outer end face and the rolling faces of the respective rolling elements 133. As a result of this, there is a possibility that an amount of wear in the contact portion between the race face formed in the present outer end face and the rolling faces of the respective rolling bodies 133 can increase and, what is worse, the present contact portion can be burnt and stuck together.
In order to solve the above problems, in Japanese Utility Model Publication No. Hei 7-35847, as shown in FIGS. 11 to 14, there is disclosed a toroidal type continuous variable transmission system which incorporates therein a thrust rolling bearing 132a improved in the lubrication performance thereof. A main body 139 of a cage 134a forming the present thrust rolling bearing 132a is formed of synthetic resin or metal such as copper or the like in a circular ring shape. In the middle portion of the main body 139 in the diameter direction thereof, in particular, at a plurality of portions thereof in the circumferential direction thereof, there are formed pockets 136 in such a manner that the pockets 136 respectively correspond in shape to rolling elements 133 to be held therein. Also, in the inner and outer faces of the main body 139, there are formed recessed grooves 140 in such a manner that they extend in the diameter direction of the main body 139 and cross the respective pockets 136; and, the recessed grooves 140 form a lubrication oil flow passage formed between the inner and outer peripheral edges of the main body 139.
According to the above-structured toroidal type continuous variable transmission system which incorporates therein the thrust rolling bearing 132a improved in the lubrication performance thereof, even when, due to the force of the lubrication oil that is jetted out from oil supply holes 138 formed in the outer race 135, the cage 134a forming the thrust rolling bearing 132a is shifted in the axial direction thereof and, as shown in FIG. 13, the inner face of the cage 134a and the outer end face of the power roller 108 are closely contacted with each other, a sufficient amount of lubrication oil are allowed to flow through the recessed grooves 140 into the pockets 136 respectively holding the rolling elements 133 therein. This prevents shortage of the lubrication oil existing in the contact portion between race faces respectively formed on the outer end faces of the power rollers 108 and the rolling faces of the rolling elements 133, which makes it possible to reduce the danger that part of the thrust rolling bearing 132a can be worn excessively or can be burnt and stuck together.
With use of the toroidal type continuous variable transmission system which is shown in FIGS. 10 to 13 and incorporates therein the thrust rolling bearing 132a improved in the lubrication performance thereof, when compared with the conventional toroidal type continuous variable transmission system, durability and reliability can be truly improved, but there are still left therein several inconveniences to be improved as follows. That is, the lubrication oil to be supplied into the pockets 136 respectively holding the rolling elements 133 therein is firstly supplied to the inner peripheral edge side of the cage 134a from the oil supply holes 138, is then allowed to flow through the respective recessed grooves 140, and is further sent into the respective pockets 136.
In particular, the lubrication oil is sent from the oil supply hole 138 into a space 141, which is formed between the power roller 108 and outer race 135 and also in which the cage 134a and rolling element 133 are disposed: that is, preferably, the thus sent lubrication oil may exist evenly over the whole periphery of the cage 134a; but, in fact, the lubrication oil exists unevenly in the peripheral direction of the cage 134a. Due to this, the amounts of the lubrication oil sent into the respective pockets 136 through the recessed grooves 40 are also uneven. Even if the amounts of the lubrication oil are slightly uneven, there can be scarcely raised a practical problem. However, if the amount of the lubrication oil that is sent into the space 141 from the oil supply hole 138 is reduced, then the amount of the lubrication oil that is sent into a certain pocket 136 becomes short, which can incur a possibility that wear in the contact portion between the rolling face of the rolling element 133 held in the present pocket 136 and its mating race face can be increased.